Earth Study 825 



CRYSTAL GROWTH 



Teacher's Story 



To watch the growth of a crystal is to witness a 

 miracle; involuntarily we stand in awe before it, 

 as a proof that of all truths mathematics is the 

 most divine and inherent in the universe. The 

 teacher will fail to make the best use of this lesson 

 if she does not reveal to the child through it some- 

 thing of the marvel of crystal growth. 



That a substance which has been dissolved in 

 water should, when the water evaporates, assem- 

 ble its particles in solid form of a certain shape, 

 with its plane surfaces set exactly at certain 



angles one to another, always the same whether ^^^ by W ' A ' 



the crystal be large or small, is quite beyond our 

 understanding Perhaps it is no more miraculous than the growth of living 

 beings, but it seems so. The fact that when an imperfect crystal, unfinished 

 or broken, is placed in water which is saturated with the same substance, it 

 will be built out and made perfect, shows a law of growth so exquisitely 

 exemplified as to again make us glad to be a part of a universe so perfectly 

 governed. Moreover, when crystals show a variation in numbers of angles 

 and planes it is merely a matter of division or multiplication. A snow 

 crystal is a six-rayed star, yet sometimes it has three rays. 



The window-sill of a schoolroom may be a place for the working of 

 greater wonders than those claimed by the astrologists of old, when they 

 transmuted baser metals to gold and worthless stones to diamonds. It 

 may be a place where strings of gems are made before the wondering eyes of 

 the children; gems fit to make necklaces for any naiad of the brook or 

 oread of the caves. 



It adds much to the interest of this lesson if different colored substances 

 are used for the forming of the crystals. Blue vitriol, potassium bichro- 

 mate, and alum give beautiful crystals, contrasting in shape as well as in 

 colors. 



Copper sulphate and blue vitriol are two names for one substance ; it is 

 a poison when taken internally and, therefore, it is best for the teacher to 

 carry on the experiment before the pupils instead of trusting the substance 

 to them indiscriminately. Blue vitriol forms an exquisitely beautiful blue 

 crystal, which is lozenge-shaped with oblique edges. Often, as purchased 

 from the drug store, we find it in the form of rather large, broken, or imper- 

 fect crystals. One of the pretty experiments is to place some of these broken 

 crystals in a saucer containing a saturated solution of the vitriol, and note 

 that they straightway assert crystal nature by building out the broken 

 places, and growing into perfect crystals. Blue vitriol is used much in the 

 dying and in the printing of cotton and linen cloths. It has quite wonderful 

 preservative qualities; if either animal or vegetable tissues are permeated 

 by it they will remain dry and unchanged. 



Potassium bichromate is also a poison and, therefore, the teacher should 

 make the solution in the presence of the class. It forms orange-red crystals, 

 more or less needle-shaped. It crystallizes so readily that if one drop of the 

 solution be placed on a saucer the pupils may see the formation of the 

 crystals by watching it for a few moments through a lens. 



